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Post by KSR Moto on Sept 28, 2018 4:14:39 GMT -5
I control air first and foremost. I do this with both my kid's bike, my Spree's and my Indian. I honestly DO NOT worry about the idle speed on initial tune. Start with recommended pilot and main jet sizes for your carb. This will typically end up being too rich, which is OK. Next I determine idle jet settings by a very easy test. I start the bike, warm it up, then test how it does from idle to a rapid blip on the throttle to 100% open. There should be no hesitation. If there is, I block off part of the air filter some more, or even tape it till throttle response improves. You are thinking too much into it on the progression circuit. While yes it does play a factor during transition, it still requires the same back pressure as the pilot jet. Again, you are looking for vacuum here. Once you get the backpressure locked in.. THEN rod it a while and read the plugs. If you have done it correctly, you should have a slightly dark plug indicating a slight rich condition. From there you step back a bit on the jetting, and then finally adjust idle mix and speed. You should end up with a bike with a proper A/F burn all through the RPM range, and your plug should be a nice milk chocolate brown. I have another carb laying aroud but i dont know what size it is, how do I measure this?
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Post by eclark5483 on Sept 28, 2018 9:13:58 GMT -5
Tape measure. No special tools required.
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Post by eclark5483 on Sept 28, 2018 11:04:30 GMT -5
i live in LA elevation 285′ and Spencer Iowa elevation is 1,312′ from what i know higher the elevation less oxygen in the air so you will need less fuel (lower jet) to get the right ratio. Well, yes and no. Hopefully I can explain this. Say for instance, we both have identical scooters with the exact same 17.5mm carb setup. Jetting for me, would tune in around the 84-86 jet range, while for you, since you need more fuel for lower elevation, your bike might be more comfortable in the 86-88 range. Now if you look at those numbers, they all fall into the range that the carb is capable of. If either of us, especially me, goes past that range on the 17.5mm carb, the carb simply can not produce the proper mix out of the venturi because of the limited mouth opening.. see what I'm saying here? Your intake will occasionally come into play here as well. A perfect example is the highly crippled Spree engine. You could get a CP adapter and run a huge ass 24mm carb on it with a gargantuan sized jet all you want. The bike will only be capable of taking in whatever the intake limits it to. Going even further into it, when all the math has been crunched, the block itself limits you. On a Spree, you are limited to an 18.5mm carb. I'm not sure where a QMB139 starts tapping out at, but all indications are that it will be somewhere in the 20mm range. Now, if you think about that, you'll understand why a 24mm will start causing issues... again, the vacuum cleaner analogy with the wide attachment comes into play. Think of the 24mm as the wide attachment, the 20mm as a standard, and the 17.5mm as the smaller attachment. All have different levels of vacuum that gets progressively tighter and stronger the smaller mouth opening you go. The trick to it, is finding the size for you, and then worry about jetting. It's a time consuming pain in the ass quite honestly. I can absolutely see the frustration in it for alot of people.
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Post by katt on Sept 28, 2018 13:20:41 GMT -5
I'll report what it looks like when i get it ordered one 24mm before you responded to the thread, also got an intake manifold for 150cc all for $26 online.
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ratdog
Scoot Enthusiast
Posts: 342
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Post by ratdog on Sept 29, 2018 13:52:43 GMT -5
First, if you have low vacuum, it isn’t because of the A9 cam. The A9 cam has les duration then a stock cam. The A9 cam also has at best the same lift, and in 75% of the ones I have measured, have less lift then the stock cam.
As far as equations to find your best jet size and working them backwards to find your best carb size...well they may be good to get you close to start, but if they worked, no one would ever do a plug chop to see what is REALY happening inside an engine. There are just to many variables to use math to figure it out. Example: what RPM are we talking about? How far above sea level. What displacement engine, is it an “ over square” or under square engine. How long is the intake track, what kind of filter! What is the exaust length and size. How much exaust pressue? And maybe most important... was this devolved for an engine attached to a CVT?
The disaAvange of larger carbs is that they don’t tend to run too good at lower RPMs. It is mostly because the air speed dropped with a larger opening.. but when you get up to 8000 rpm, air speed is no longer a problem. Now if you want to run your engine in the 7500 rpm range it was designed for, then, frankly, the 18 mm carb is fine. If you want more hp, then you have to move that power peak up the RPM range. Now these little engines are not really made to run at 9000-11000 rpm. Based on the engines I have worked on, I would say you have to be up in that 10,000 rpm range to “ need” a 24mm. In the engines we have build, with the very mild cams that are generally advaible, we find a 22 mm to be the biggest that improves preformance. We have tried 23mm carbs, but had no measurable increese in preformance. I have not tried any 24 mm carbs because we had no inprovment with the 23.
My personal thoughts, if you are going to a larger carb, get the all metal intake manifold. It’s much easier to get a proper port match with the metal manifold
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Post by katt on Sept 29, 2018 14:14:50 GMT -5
First, if you have low vacuum, it isn’t because of the A9 cam. The A9 cam has les duration then a stock cam. The A9 cam also has at best the same lift, and in 75% of the ones I have measured, have less lift then the stock cam. I have not measured, but description for A9 claims it opens valves more and keeps them open longer this is why i got it in the first place. And i started having this after i installed A9 cam.
For me 24mm was choice because its cheaper than 20mm and because i want to use it for 150cc engine later.
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ratdog
Scoot Enthusiast
Posts: 342
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Post by ratdog on Sept 29, 2018 14:40:37 GMT -5
Well you information on the A9 cam is incorrect. It’s one of those things where one person posts it, then others replete it, and suddenly it is a “fact”. If you look at the post on the A9 cams, I have the real measurements for several different “A9” cams. Non of them have more duration, and none of them have more lift. The A9 cam is what we used to call a “Tourque grind”. ( except every other tourque cam I have ever seen increases lift over stock.
As you already ordered the 24 mm, I guess the question is no longer valid, and it really dosent matter what advice we give you. Because you have the engine connected to a CVT, putting “too much” carb most likely won’t hurt you because the CVT keeps you up in the 7500 rpm range from a few mph to near top speed. I would recommend you change your oil often as I would bet you will have gas leaking into your oil, but that’s just a guess. Just my personal thought, I would set the idle high, like 2500 rpms to make it a bit easier to live with. My guess will be that you will have to go leaner on the jet, but until you have it on the engine and have a few miles on it, we really won’t know.
The most common result of too rich jetting will be that it gets to a certain rpm then falls on its face. I tend to run street engines on the rich side because they run a lot cooler, and these little guys run so hot, esp with a BBK, that they can use all the help they can get.
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ratdog
Scoot Enthusiast
Posts: 342
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Post by ratdog on Sept 29, 2018 14:48:57 GMT -5
K. long post about cams, hope you can stay awake to the end Cam #1 stock from a new icebear 50cc falcon “CX” on the gear. “6002/p6” on the bearings. Two small holes one large hole Cam #2 Glixal A9 AT-A9 on gear, 16002 and 'XS” on bearings. 9 holes plus the two small timing holes Cam #3 OCC Performance cam A9 3 hole like stock 6002/p6 on bearings Cam #4 Fly Pig performance cam A9 oval with “S” thru it on gear 6002/P6 on bearings three hole like stock cam Cam #5 cam made it Taiwan Sorta a teardrop inside of teardrop graphic on gear three holes like stock Cam #1 lift, .187” on intake .179 on exhaust lift at TDC on intake stroke .008 intake .026 on exhaust duration intake @.001 162.2 @.005 122.7 exhaust @.001 161.2 @.005 152.8 cam #2 lift .187 on intake .179 on exhaust lift at TDC on intake stroke .004 intake .021 on exhaust duration intake @.001 156 @.005 135.2 exhaust @.001 150.8 @.005 119.6 cam #3 lift .187 on intake .182 on exhaust lift at TDC on intake stroke .009 intake .030 exhaust duration intake @.001 176.8 @.005 171.6 exhaust @.001 145.6 @.005 140.4 cam #4 lift .182 on intake .176 on exhaust lift at TDC on intake stroke .020 on intake .010 on exhaust duration intake at .001 156 @.005 119.6 exhaust at .001 145.6 @.005 119.6 cam #5 lift .186 on intake .179 on exhaust lift at TDC on intake stroke .006 on intake .022 on exhaust duration intake at .001 159 @.005 139.3 exhaust at .001 153.2 @.005 121.2 Read more: 49ccscoot.proboards.com/thread/23504/important-info-gilxal-a9-cam#ixzz5SWQebPCJ
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Post by katt on Sept 29, 2018 14:52:24 GMT -5
I dunno what most of it means sorry. I got 24mm carb already that was quick will try it on now and tell you the results.
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ratdog
Scoot Enthusiast
Posts: 342
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Post by ratdog on Sept 29, 2018 14:52:26 GMT -5
K. long post about cams, hope you can stay awake to the end Cam #1 stock from a new icebear 50cc falcon “CX” on the gear. “6002/p6” on the bearings. Two small holes one large hole Cam #2 Glixal A9 AT-A9 on gear, 16002 and 'XS” on bearings. 9 holes plus the two small timing holes Cam #3 OCC Performance cam A9 3 hole like stock 6002/p6 on bearings Cam #4 Fly Pig performance cam A9 oval with “S” thru it on gear 6002/P6 on bearings three hole like stock cam Cam #5 cam made it Taiwan Sorta a teardrop inside of teardrop graphic on gear three holes like stock Cam #1 lift, .187” on intake .179 on exhaust lift at TDC on intake stroke .008 intake .026 on exhaust duration intake @.001 162.2 @.005 122.7 exhaust @.001 161.2 @.005 152.8 cam #2 lift .187 on intake .179 on exhaust lift at TDC on intake stroke .004 intake .021 on exhaust duration intake @.001 156 @.005 135.2 exhaust @.001 150.8 @.005 119.6 cam #3 lift .187 on intake .182 on exhaust lift at TDC on intake stroke .009 intake .030 exhaust duration intake @.001 176.8 @.005 171.6 exhaust @.001 145.6 @.005 140.4 cam #4 lift .182 on intake .176 on exhaust lift at TDC on intake stroke .020 on intake .010 on exhaust duration intake at .001 156 @.005 119.6 exhaust at .001 145.6 @.005 119.6 cam #5 lift .186 on intake .179 on exhaust lift at TDC on intake stroke .006 on intake .022 on exhaust duration intake at .001 159 @.005 139.3 exhaust at .001 153.2 @.005 121.2 Read more: 49ccscoot.proboards.com/thread/23504/important-info-gilxal-a9-cam#ixzz5SWQebPCJ
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Post by eclark5483 on Sept 29, 2018 15:24:42 GMT -5
If you must insist on trying it out, I URGE YOU to pay careful attention to the filter system you use for it. You are for sure, going to lose bottom end, so you'll absolutely wanna play around with back pressures on the air filter. Tuning that will help pick up a bit of that slack. 24mm is certainly not optimal, but if you got the damn thing anyway, I'm sure all of us here can help you get the tune on it down.
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Post by eclark5483 on Sept 29, 2018 15:43:49 GMT -5
Also, I agree with ratdog... READ THE PLUG. Buy tons of plugs, be prepared to destroy them to get it all right!!
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Post by katt on Sept 29, 2018 19:14:19 GMT -5
My old carb is 18.5mm doh i thought it was 17.5mm :/
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Post by katt on Sept 29, 2018 21:11:51 GMT -5
Okay i managed to put it on yeah size #45 idle jet was overkill it was white smoke coming out the exhaust and spark plug glow black in few minutes plus knocking.
it come with something small like 37ish so i just put stock idle jet and smallest main jet i had which is #90 Another problem throttle cable was too short i had to extend it bit. I put zero resistance filter cuz stock would not fit on that monster carb. Now about performance its way better like someone gave this engine suddenly gained like 30% percent more power. Not saying its better than 20mm carb, but obviously better than my old 18.5mm carb, i will do speed and acceleration tests later when traffic goes down
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ratdog
Scoot Enthusiast
Posts: 342
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Post by ratdog on Sept 30, 2018 11:21:28 GMT -5
The advantage of the CVT trans! Your engine, for the most part, only has to “pull” from about 7500 rpms up. The big carb is pushing that power up the rpm range. Just guessing, but I’ll bet your engine is pulling a LOT more RPM now
Now run the bike at WOT for a bunch and avoid idleing. If possible make a run home at WOT and keep the throttle wide open while you shut off the motor and come to a stop. Then pull the plug and take a pic so we can clearly see the insulator (white part)
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